U.S. patent application number 10/396722 was filed with the patent office on 2004-03-18 for magnetic recording medium and magnetic recording/reproducing system.
Invention is credited to Jingu, Nobuhiro, Watase, Shigeharu.
Application Number | 20040053074 10/396722 |
Document ID | / |
Family ID | 29233720 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040053074 |
Kind Code |
A1 |
Jingu, Nobuhiro ; et
al. |
March 18, 2004 |
Magnetic recording medium and magnetic recording/reproducing
system
Abstract
The present invention provides a magnetic recording medium
having a thinned film back coating layer as well as suppressed
tribocharging by sliding to the tape guide pin on running, and
having excellent running durability. The present invention also
provides a magnetic recording/reproducing system using the magnetic
recording medium above. A magnetic recording medium 1 which
comprises at least a magnetic layer 3 and a protective layer 4
comprising a hard film containing carbon as a principal component
in this order on one surface of a non-magnetic support 2, and
comprises a metal layer 7 from 1 to 50 nm in thickness and a back
coating layer 6 comprising a hard film containing carbon as a
principal component in this order on the other surface of said
non-magnetic support 2. A magnetic recording/reproducing system,
for recording and reproducing a tape-like magnetic recording medium
above, by using a magnetic recording/reproducing device having a
member on which said hard film containing carbon as a principal
component is formed at parts in contact with a surface of said back
coating layer.
Inventors: |
Jingu, Nobuhiro; (Hita-shi,
JP) ; Watase, Shigeharu; (Hita-shi, JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING
1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Family ID: |
29233720 |
Appl. No.: |
10/396722 |
Filed: |
March 26, 2003 |
Current U.S.
Class: |
428/837 ;
428/835; G9B/5.288; G9B/5.299 |
Current CPC
Class: |
G11B 5/65 20130101; G11B
5/8404 20130101; G11B 5/735 20130101 |
Class at
Publication: |
428/694.0BB ;
428/694.00R |
International
Class: |
B32B 019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2002 |
JP |
2002-087575 |
Claims
What is claimed is:
1. A magnetic recording medium which comprises at least a magnetic
layer and a protective layer comprising a hard film containing
carbon as a principal component in this order on one surface of a
non-magnetic support, and comprises a metal layer from 1 to 50 nm
in thickness and a back coating layer comprising a hard film
containing carbon as a principal component in this order on the
other surface of said non-magnetic support.
2. The magnetic recording medium according to claim 1, wherein said
magnetic layer is a metal thin film type magnetic layer.
3. The magnetic recording medium according to claim 1, wherein said
back coating layer comprising said hard film containing carbon as a
principal component is formed by a vacuum film forming method.
4. The magnetic recording medium according to claim 1, wherein said
back coating layer has a thickness of from 3 to 300 nm.
5. The magnetic recording medium according to claim 1, wherein said
metal layer is formed by employing, as a raw material, at least one
selected from the group consisting of Al, Ag, Cr, Cu, Mn, Ti, Co,
Ni, Zn, and alloys of said metals.
6. The magnetic recording medium according to claim 1, wherein the
electric resistivity of said metal layer is in the range of from
10.sup.-2 to 10.sup.10 .OMEGA..multidot.cm.
7. The magnetic recording medium according to claim 1, which
further comprises a lubricant layer on said protective layer.
8. The magnetic recording medium according to claim 1, which
further comprises a lubricant layer on said back coating layer.
9. A magnetic recording/reproducing system, for recording and
reproducing a tape-like magnetic recording medium according to
claim 1, by using a magnetic recording/reproducing device having a
member on which the hard film containing carbon as a principal
component is formed at parts in contact with a surface of said back
coating layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magnetic metal thin film
type magnetic recording medium and to a magnetic
recording/reproducing system.
[0003] 2. Disclosure of the Related Art
[0004] With progress in information society, magnetic recording
media capable of recording data at higher density are keenly
demanded, and advances in magnetic recording layers,made a shift
from the coated type to the so-called magnetic metal thin film
type. Since being free from binders as the coated type magnetic
recording media in the magnetic layer, the magnetic metal thin film
type recording media yield high saturation magnetization and are
suitable for high density recording. In the case of magnetic metal
thin film type media, used Co--Ni alloys, Co--Cr alloys, Co--O
alloys, and the like as the magnetic metals which are directly
deposited by means of plating or vacuum thin film forming methods
(such as vacuum deposition method, sputtering method, ion-plating
method, and the like) on a non-magnetic support such as polyester
film, polyamide film, polyimide film, and the like.
[0005] The most notable characteristic of long thin film media is
that the recording capacity can be easily increased by elongating
the winding length. However, due to the explosive increase in the
amount of information in recent years, data storage tape with
further increased capacity is demanded. In order to increasing the
number of tape turns to cope with this requirement, method for
enlarging the winding diameter, or for thinning the tape thickness
are conceivable. The former results in necessity for re-designing
not only the diameter of the reel, but also the cassette casing,
and this leads to a considerable increase in production cost. On
the other hand, the latter requires thinning the thickness of the
film constructing the tape.
[0006] To take a tape formed by vacuum deposition which makes
advance in thinning tape thickness as an example, a deposited film
to be the recording layer has a thickness of about 200 nm, and the
carbon-based protective film deposited thereon as a protective
layer has a thickness of about 10 nm, a further thinning of these
films has little contribution in decreasing the total tape
thickness. In contrast to this, the support film has a thickness of
about 5 .mu.m, and the back coating layer on the side of running
surface has a thickness of about 0.5 .mu.m, and, an increase in the
number of turns, i.e., an increase in capacity, can be expected by
thinning these layers. However, a decrease in support film
thickness leads to a lowered tape stiffness, and this unfavorably
influences the recording/reproducing characteristics. Thus, it is
believed most preferable to thin the back coating layers for
reducing the tape thickness.
[0007] Back coating layers are generally formed by coating a
support film surface with a coating material prepared from a
material containing carbon black, inorganic pigments (such as
calcium carbonate) and the like, and a solvent. However, by taking
the coating technique into consideration in view of productivity,
it becomes difficult to control the thickness of the back coating
layer with high precision as the back coating layer thickness thins
down.
[0008] In place of forming the back coating layer by coating,
Japanese Patent Laid-Open No. 54935/1997 discloses a magnetic
recording medium comprising double layered back coating layer
comprising a 80 nm thick diamond-like carbon (DLC) thin film and on
the support and a 90 nm thick graphite thin film on the
diamond-like carbon thin film. Since a diamond-like carbon thin
film has poor electric conductivity, and decreases tribocharging by
sliding to the tape guide pin on running, a graphite thin film is
provided thereon as a solid lubricant. However, in the case
graphite thin film is provided on the sliding surface, friction in
molecular level occurs to cause unfavorable dropouts due to the
generation of particulates.
[0009] In Japanese Patent No. 2,638,113 disclosed is a magnetic
recording media having a back coating layer comprising diamond-like
carbon thin film formed on a fine-particle coated layer on a
support. In order to reduce tribocharging due to sliding by the
diamond-like carbon thin film, a fine-particle coated layer is
provided as an undercoat layer. However, it requires providing a
back coating layer comprising diamond-like carbon thin film on the
undercoat layer with a thickness of about 0.4 .mu.m on the support,
and this cannot contribute to thin the tapes.
[0010] Furthermore, on forming a diamond-like carbon thin film
directly on the non-magnetic support, since the non-magnetic
support is fundamentally an electric insulating material, there is
another problem that the film growth rate is extremely decreased in
the case methods where charged particles such as plasma CVD and ion
plating are nucleus of film growth.
[0011] As described above, the technique is yet to be realized for
replacing the coating type back-coating layer, which is difficult
to control the thin film thickness with high precision, with a back
coating layer comprising diamond-like carbon thin film, although it
is believed effective in thinning the total thickness of the
tapes.
[0012] Furthermore, by thinning the back coating layer as
diamond-like carbon thin film, the support film thickness can be
increased at the expense of thinning the back coating layer in the
case the total tape thickness is made the same as above. The lowest
of the strength per unit thickness in data storage tapes at present
is the back coating layer of a coated type, and by increasing the
thickness of the support film brought by thinning the back coating
layer, the strength of the tape as a whole can be increased to
improve durability.
[0013] On the other hand, in Japanese Patent Laid-Open Nos.
44841/1997, 102051/1996, and 2000-339661 disclosed are an attempt
of replacing the back coating layer with a metal thin film in order
to compensate for tape stiffness by reducing the thickness of the
tape. However, in the case vacuum deposition method, which is
believed to yield relatively high production efficiency, is
employed for the production of metal thin film, the non-magnetic
supports are limited to those resistant to a large thermal load
such as radiation heat from evaporation sources or solidification
heat of deposited particles, such as polyaramid supports. In the
case supports with relatively low heat resistance, such as PET or
PEN, are used, the supports must be made sufficiently thick, and
this results in retrogressing against thinning of the film.
SUMMARY OF THE INVENTION
[0014] In light of such circumstances, there is demanded a
technology of thinning the back coating layer by using diamond-like
carbon thin film, further suppressing the generation of
tribocharging attributed to diamond-like carbon thin film.
[0015] Accordingly, an object of the present invention is to
provide a magnetic recording medium having a thinned film back
coating layer as well as suppressed tribocharging by sliding to the
tape guide pin on running, and having excellent running durability.
Another object of the present invention is to provide a magnetic
recording/reproducing system using the magnetic recording medium
above.
[0016] The present inventors have extensively and intensively
conducted studies, and as a result, they have found that the above
objects can be achieved by providing, via a metallic layer on a
support, a back coating layer comprising a hard film containing
carbon as a principal component. The present invention has been
accomplished based on these findings.
[0017] The present invention provides a magnetic recording medium
which comprises at least a magnetic layer and a protective layer
comprising a hard film containing carbon as a principal component
in this order on one surface of a non-magnetic support, and
comprises a metal layer from 1 to 50 nm in thickness and a back
coating layer comprising a hard film containing carbon as a
principal component in this order on the other surface of the
non-magnetic support.
[0018] The present invention provides-above magnetic recording
medium, wherein the magnetic layer is a metal thin film type
magnetic layer.
[0019] The present invention provides above magnetic recording
medium, wherein the back coating layer comprising the hard film
containing carbon as the principal component is formed by a vacuum
film forming method.
[0020] The present invention provides above magnetic recording
medium, wherein the back coating layer has a thickness of from 3 to
300 nm.
[0021] The present invention provides above magnetic recording
medium, wherein the metal layer is formed by employing, as a raw
material, at least one selected from the group consisting of Al,
Ag, Cr, Cu, Mn, Ti, Co, Ni, Zn, and alloys of the metals.
[0022] The present invention provides above magnetic recording
medium, wherein the electric resistivity of the metal layer is in
the range of from 10.sup.-2 to 10.sup.10 .OMEGA..multidot.cm.
[0023] The present invention provides above magnetic recording
medium, which further comprises a lubricant layer on the protective
layer.
[0024] The present invention provides above magnetic recording
medium, which further comprises a lubricant layer on the back
coating layer.
[0025] The present invention provides a magnetic
recording/reproducing system, for recording and reproducing a
tape-like magnetic recording medium above, by using a magnetic
recording/reproducing device having a member on which the hard film
containing carbon as a principal component is formed at parts in
contact with a surface of the back coating layer.
[0026] In the present invention, "containing carbon as a principal
component" signifies that content of atomic carbon in the film is
from 60 to 80%, and in general, hydrogen is contained in the film
in addition to carbon. The atomic ratio of hydrogen to carbon (H/C)
is preferably in a range of from 0.25 to 0.66. "To be hard film"
means, specifically, that to be a film having a Vicker's hardness
of 6370 N/mm.sup.2 (650 kg/mm.sup.2) or higher, and this hardness,
as expressed by refractive index, corresponds to a value of 1.9 or
higher. A film having such a refractive index is known that the
hardness can be approximated from the refractive index. For
instance, when a refractive index is 1.9the Vicker's hardness is
6370 N/mm.sup.2 (650 kg/mm.sup.2). There is especially no upper
limit in refractive index, but is about 2.25, and it corresponds to
Vicker's hardness of 29400 N/mm.sup.2 (3000 kg/mm.sup.2). As a
method for obtaining approximate value of hardness from refractive
index, there may be mentioned measuring the refractive index of the
hard film with an ellipsometer, while measuring vicker'shardness
with micro hardness meter (manufactured by NEC Corporation), and
preparing a calibration curve in advance to find the value of
hardness from the refractive index. Furthermore, such hard films
are amorphous, or form a continuous phase that is nearly amorphous,
and yield broad peaks at 1,560 cm.sup.-1 and 1,330 cm.sup.-1 when
measured by Raman spectroscopy. The term hard carbon film or DLC
film is employed hereinafter in the sense of "hard films containing
carbon as a principal component".
[0027] According to the present invention, there is provided a
magnetic recording medium having a thinned film back coating layer
as well as suppressed tribocharging by sliding to the tape guide
pin on running, and having excellent running durability. Also
according to the present invention, there is provided a magnetic
recording/reproducing system using the magnetic recording medium
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a cross section view showing an example of layer
constitution of a magnetic recording medium according to the
invention.
[0029] FIG. 2 is a cross section view showing an example of layer
constitution of a magnetic recording medium according to the
invention.
[0030] FIG. 3 is a schematic drawing of an apparatus for measuring
slide friction coefficient.
[0031] FIG. 4 is an explanatory drawing showing the method for
measuring cupping.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The magnetic recording medium according to the invention is
described below by making reference to FIGS. 1 and 2.
[0033] FIGS. 1 and 2 are each cross section views showing an
example of layer constitution of a magnetic recording medium
according to the invention. Referring to FIG. 1, a magnetic
recording medium (1) comprises, on the surface of one side of a
non-magnetic support (2), a magnetic layer (3), a protective layer
(4) comprising a hard carbon film, and a lubricant layer (5) in
this order; and comprises, on the surface of the other side of the
non-magnetic support (2), a back coating layer (6) comprising a
hard carbon film, with a metal layer (7) intervening between them.
In the example of FIG. 2, the magnetic recording medium (1) further
has a lubricant layer (8) on the back coating layer (6).
[0034] There is no particular limitation concerning the material
for the non-magnetic support (2), and is selected from resins such
as polyester-based resins such as polyethylene terephthalate (PET)
and polyethylene naphthalate (PEN), polyamide-based resins such as
aromatic polyamides, and olefin-based resins such as polyethylene
and polypropylene. The thickness of the non-magnetic support is
selected from a range from 3 to 12 .mu.m, depending on aimed time
for imaging-recording or recording, or the like. In order to make
the entire tape thinner, in particular, the thickness of the
non-magnetic support is preferably selected from a range of 3 to 6
.mu.m.
[0035] The magnetic layer (3) is formed on the surface of one side
of the non-magnetic support (2) by means of vapor film forming
methods such as vacuum deposition and ion plating. As the magnetic
materials, used are Co or an alloy containing Co, such as Co--Ni,
Co--Cr, Co--O, Fe--Co--Ni, Co--Pt, Co--Fe, and the like. In the
case of vapor film forming such as vacuum deposition, those having
similar boiling points are in the form of alloy, and those having
different boiling points are subjected to multi-element vacuum
deposition. In the case of sputtering and the like, on the other
hand, metal or alloys are subjected to film forming as they are. A
tape-like medium is subjected to oblique vapor film forming.
[0036] For the vacuum deposition of the magnetic layer, the
magnetic material is molten by an electron gun after evacuating the
inside of the vacuum deposition chamber to about 10.sup.-5 Torr,
and the non-magnetic support is run along a cooled main roller
(cooling can) at the point the entire magnetic material is molten,
such that the vapor deposition may be initiated at the main roller
part. In order to control the magnetic characteristics, an
oxidizing gas selected from oxygen, ozone, and nitrous oxide may be
introduced to the magnetic layer. In a long extended medium,
oblique film forming is performed, such that the column is set to
make an angle of 20 to 50 degrees with respect to the non-magnetic
support. In the case of a vertical medium, on the other hand, the
crucible is set just below the can to set the aperture portion of
the mask at an angle within .+-.10 degrees.
[0037] The magnetic layer is a mono-layered or a multi-layered
constitution. The thickness of the magnetic layer is in a range of
about 0.01 to 0.5 .mu.m.
[0038] A hard carbon film (DLC film) as a protective layer (4) is
formed on the magnetic layer (3) by means of CVD or sputtering
method. Both sputtering and CVD methods are processes using charged
particles. Sputtering method is a physical process; firstly an
inert gas such as gaseous Ar and the like is ionized (plasma
generation) by using an electric field or a magnetic field, further
the thus ionized argon ion is accelerated to knock out the target
atoms by the kinetic energy, and the knocked out atoms are
deposited on the substrate disposed opposed to the target to form
the desired film. The film forming rate of DLC film using
sputtering method is generally low, and it is a means of film
forming inferior in productivity from industrial viewpoint. On the
other hand, CVD method causes chemical reactions such as
decomposition, synthesis, and the like of gas to be raw material
using the energy of the plasma generated by ionization or magnetic
field to thereby form a film. In the invention, there is no problem
in using sputtering method, but preferred is CVD method capable of
forming films at high speed.
[0039] As the gas for use in CVD method, those which are in the
gaseous state under ordinary temperature and pressure, such as
methane, ethane, propane, butane, ethylene, propylene, and
acetylene, are easy for handling, or there is also, no problem in
using liquid starting materials.
[0040] The gas above is introduced in a reaction system, high
frequency is applied to generate plasma state, and vapor phase film
forming is carried out. More specifically, in a chamber (vacuum
cell) provided with supply roller, take-up roller, main roller
equipped with partial cylindrical face electrode plates (with
circular arc-shaped cross section) for plasma polymerization
opposed to each other at a distance, and path roller if necessary,
the starting material roll (wound non-magnetic support with a vapor
deposited ferromagnetic metal into roll) is set on the supply
roller, and then evacuate the chamber to a pressure as low as
10.sup.-5 Torr or lower, followed by performing plasma
polymerization with introducing gaseous hydrocarbon at a
predetermined amount such that the reaction pressure in a range of
1 to 10.sup.-2 Torr would be achieved. The amount of the gas
introduced is set optionally as required, because it depends on the
size of the chamber.
[0041] There is no particular restriction concerning high
frequency, however, stable discharge easy for handling is obtained
in the range of from around 1 kHz to 1 MHz. At frequencies lower
than 1 kHz, it is difficult to form film for a long time, and at
frequencies higher than 1 MHz, it is not easy to obtain hard films.
The range easy to operate is preferably in the range from about 50
kHz to 450 kHz. The film thickness of the hard carbon film is in a
range of from 2 to 20 nm, and preferably in a range of around from
5 to 10 nm. A film thinner than 2 nm cannot exhibit its function as
a protective film, on the other hand, films thicker than 20 nm
suffer problems of spacing loss.
[0042] Since the lubricants are coated on the DLC film with
difficulty, post-treatment may be performed after forming the DLC
film. The post-treatment is preferably carried out by using gaseous
oxygen or a gas containing oxygen, and usable gases are, for
instance, oxygen, air, and gaseous carbon dioxide. The post
treatment is easily performed by a procedure similar to that for
forming DLC film. The frequency range for use in post-treatment is
preferably in the range of from 1 kHz to 40 MHz like in forming DLC
films, and particularly, effects are easily displayed in the range
of from 50 kHz to 13.56 MHz.
[0043] A lubricant layer (5) is formed on the hard carbon
protective layer (4) by coating. As the lubricant, a lubricant
containing fluorine, a hydrocarbon based ester, or a mixture of
these may be used.
[0044] The lubricant is, for instance, those having a basic
structure expressed by R.sup.1-A-R.sup.2, where,
[0045] R.sup.1: CF.sub.3(CF.sub.2)n--,
CF.sub.3(CF.sub.2).sub.n(CH.sub.2).- sub.m--,
CH.sub.3(CH.sub.2).sub.1--, or H;
[0046] A: --COO--, --O--, or
--COOCH(C.sub.1H.sub.21+1)CH.sub.2COO--; and
[0047] R.sup.2: CF.sub.3(CF.sub.2).sub.n--,
CF.sub.3(CF.sub.2).sub.n(CH.su- b.2).sub.m--,
CH.sub.3(CH.sub.2).sub.1--, or H; provided that preferably R.sup.1
differs from R.sup.2, and n satisfies a numeral in a range of from
7 to 17, m from 1 to 3,and 1 from 7 to 30. Furthermore, higher
lubricating effect is displayed in the case R.sup.1 and/or R2 are
straight-chain group. In the case n is smaller than 7,
water-repelling properties become low, and in the case n is larger
than 17, friction cannot be lowered because blocking phenomenon
occurs between the lubricant and the non-magnetic support or the
back coating layer. Particularly preferred among them is a
lubricant containing fluorine. Furthermore, two or more of these
lubricants may be mixed.
[0048] A coating solution is prepared by dissolving these
lubricants in a solvent such as ketones, hydrocarbons, and
alcohols. As the ketones, there may be mentioned acetone, methyl
ethyl ketone (MEK), methyl isobutyl ketone, cyclohexanone, diethyl
ketone, and the like. As hydrocarbons, examples include normal- and
iso-hydrocarbons such as hexane, heptane, octane, nonane, decane,
undecane, and dodecane. Alcohols include methanol, ethanol,
propanol, and isopropanol. Thus prepared coating solution is
applied on the hard carbon protective layer (4) and dried to
provide the lubricant layer (5). The thickness of the lubricant
layer (5) is not to be measured accurately, but it is believed to
be about several nanometers. The amount of lubricant may be
controlled by the concentration of the coating solution. Forming of
the lubricant layer (5) by coating may be performed after forming
the back coating layer (6) comprising hard carbon film, which is
later stated.
[0049] A metal layer (7) is formed on the surface of the other
surface of the non-magnetic support (2). The metal layer (7) is
preferably a metal thin film formed from a non-magnetic metallic
material having no influence on the recorded information provided
on the magnetic surface. In the case magnetic material such as Co
and the like is used, it is necessary nearly to demagnetize it by
turning into an oxide and the like. The metal layer (7) may be
formed by a generally known vacuum thin film forming methods such
as vacuum deposition method, sputtering method, ion-plating method,
and the like. Since the metal thin films formed by such vacuum film
forming methods are generally high in chemical activity, the method
for lowering the activity by introducing an oxidizing gas such as
oxygen into the films formed. Usable as metal materials are, for
instance, Al, Ag, Cr, Cu, Mn, Ti, Co, Ni, Zn, and alloys of said
metals and the like; in view of production efficiency of film
forming, preferred are metal materials of low melting points, and
ideal ones are, for example, Al and Al based alloys.
[0050] The metal layer (7) has a thickness of 1 to 50 nm,
preferably, 1 to 40 nm, and more preferably, 10 to 40 nm. In the
case the film thickness of the metal layer (7) exceeds 50 nm,
unbalance occurs on the stress between the magnetic surface side
and the tape running surface side, which results in an increase in
tape cupping and a problem of decreasing in running stability. On
the other hand, in the case the film thickness of this layer is
less than 1 nm, the function of electric conductivity is impaired.
From the viewpoint of film forming, a film with a thickness as thin
as 1 to 50 nm reduces the problem of thermal load on the
non-magnetic support on performing film forming, and supports
comprising a material having relatively low heat resistance such as
a PET and PEN may be sufficiently used.
[0051] The electric resistivity of the metal layer (7) is in a
range of from 10.sup.-2 to 10.sup.10 .OMEGA..multidot.cm,
preferably, it is in a range of 10.sup.-2 to 10.sup.7
.OMEGA..multidot.cm, and must be lower than that of the back
coating layer (6) by at least one order of magnitude. Since-the
metal layer (7) has such an electric conductivity, a desired
electric conductivity can be maintained for the back coating layer
(6) comprising hard carbon film formed on metal layer (7).
Furthermore, the rate of film forming of the hard carbon films can
be improved at the same time.
[0052] A hard carbon film (DLC film) as the back coating layer (6)
is formed on the metal layer (7) in the same manner as in the case
of the hard carbon protective layer (4).
[0053] The back coating layer (6) has at a thickness of about 3 to
300 nm, preferably, about 5 to 50 nm, and more preferably, about 5
to 10 nm. The DLC film is a carbon film higher in hardness, and it
sufficiently functions as back coating with such a thickness. In
the case the film thickness is less than 3 nm, the strength of the
DLC film becomes insufficient to cause instability on the
resistance against scratches.
[0054] An ordinary DLC film suffers low electric conductivity.
[0055] However, in the present invention, the back coating layer
(6) comprising DLC film is formed on the metal film (7). Hence, the
electric conductivity of the DLC film is higher as compared with
that of a generally known DLC film. Accordingly, although in the
magnetic recording medium of the present invention the back coating
layer (6) comprises DLC film, the tribocharging that generates on
the running tape due to sliding on the guide pin is considerably
suppressed to exhibit excellent running durability. In this manner,
a magnetic recording medium having a thinned film back coating
layer (6) is obtained.
[0056] In the invention, a lubricant layer (8) may be further
formed on the back coating layer (6). The lubricant layer (8) may
be formed in a manner similar to the case of lubricant layer (5)
formed on the protective layer (4) by using a similar material. The
thickness of the lubricant layer (8) is not to be measured
accurately, but it is believed to be about several nanometers.
[0057] On recording and reproducing the tape-like magnetic
recording medium according to the present invention, an ordinary
magnetic recording/reproducing device may be used. In an ordinary
magnetic recording/reproducing device, various types of
tape-sliding members such as tape guides and tape controlling
guides are generally having stainless steel. In the magnetic
recording medium of the present invention, tribocharging due to
sliding against the members on running is considerably suppressed,
hence, favorable recording/reproducing as well as excellent running
durability can be obtained by using an ordinary magnetic
recording/reproducing device.
[0058] However, since the back coating layer is DLC film in the
magnetic recording medium of the present invention, in the case a
magnetic recording/reproducing device comprising various members on
which a hard carbon film is formed (which is sometimes referred to
hereinafter as "DLC film coated treatment") on the portion (or the
surface) in contact with the surface of the back coating layer,
i.e., the tape running surface is used, the friction coefficient on
sliding the tape running surface on the various members is further
lowered, and the tribocharging is further suppressed. The film
thickness of the DLC film on the surface of the metallic various
members may be about 1 .mu.m; i.e., a thickness generally applied
to tools and the like. By coating DLC films at such a thickness,
friction properties can be sufficiently improved. Accordingly, the
present invention also relates to a magnetic recording/reproducing
system for recording and reproducing tape-like magnetic recording
medium of the present invention, which uses a magnetic
recording/reproducing device equipped with members on which hard
carbon films is formed at parts that are brought into contact with
the surface of the back coating layer.
EXAMPLES
[0059] The invention is described further concretely by way of
examples below, but it should be understood that the invention is
not limited thereto.
Example 1
[0060] A magnetic recording medium of the layer constitution shown
in FIG. 1 was prepared by the following process.
[0061] A PEN film (2) 4.7 .mu.m in thickness was used as a
non-magnetic support. On one surface of the PEN film (2), a
ferromagnetic thin film of Co was formed by oblique vacuum
deposition to obtain a 0.1 .mu.m thick magnetic layer (3). Then, on
the magnetic layer (3), a protective layer (DLC film) (4) having a
10 nm thick hard carbon film was formed by means of plasma CVD
method. Post-treatment (plasma treatment) was performed to the DLC
film by using gaseous O.sub.2.
[0062] Subsequently, by vacuum deposition, about 10 nm thick metal
layer (7) was formed using Al on the surface of PEN film (2)
opposite to the surface where the magnetic layer (3) is formed. In
this case, vacuum deposition was carried out while supplying oxygen
gas in order to lower the chemical activity of the film. Then, a
back coating layer (DLC film) (6) having 10 nm thick hard carbon
film was formed on the metal layer (7) by means of plasma CVD
method.
[0063] Furthermore, on the protective layer (4), a lubricant
coating solution is coated by dye nozzle method, and was dried to
form a 5 nm thick lubricant layer (5). The resulting product was
then cut to 8-mm width to obtain a magnetic tape sample having a
total thickness of about 4.8 .mu.m.
[0064] The lubricant coating solution was a solution obtained by
dissolving a fluorine-containing compound of succinic acid
derivative and a fluorine-containing compound of aliphatic ester
shown below at the same mass amounts in a 1/2/7 mixed solvent of
MEK/hexane/ethanol.
HOOCCH(C.sub.14H.sub.29)CH.sub.2COOCH.sub.2CH.sub.2(CF.sub.2).sub.7CF.sub.-
3
CH.sub.3(C.sub.16H.sub.32)COOCH.sub.2CH.sub.2(CF.sub.2).sub.7CF.sub.3
(lubricant)
Example 2
[0065] Shown in FIG. 2, a magnetic tape sample was prepared in the
same manner as in Example 1, except for additionally forming a
lubricant layer (8) on the back coating layer (6). The lubricant
layer (8) was formed in the same manner as in the case of lubricant
layer (5).
Example 3
[0066] A magnetic tape sample was prepared in the same manner as in
Example 1, except for changing the thickness of the metal layer (7)
to 30 nm.
Example 4
[0067] A magnetic tape sample was prepared in the same manner as in
Example 1, except for changing the thickness of the metal layer (7)
to 40 nm.
Example 5
[0068] A magnetic tape sample was prepared in the same manner as in
Example 1, except for using Co as the material for the metal layer
(7).
Example 6
[0069] A magnetic tape sample was prepared in the same manner as in
Example 1, except for changing the thickness of the back coating
layer (6) to 100 nm.
Comparative Example 1
[0070] A magnetic tape sample was prepared in the same manner as in
Example 1, except for not forming the metal layer (7), but directly
forming a back coating layer (6) (a thickness of 10 nm) on the
surface of PEN film (2) opposite to the surface where the magnetic
layer (3) is formed.
Comparative Example 2
[0071] A magnetic tape sample was prepared in the same manner as in
Example 1, except for not forming the back coating layer (6), but
forming the metal layer (7).
Comparative Example 3
[0072] A magnetic tape sample was prepared in the same manner as in
Example 1, except for not forming the metal layer (7), but directly
forming a back coating layer.(6) at a thickness of 100 nm on the
surface of PEN film (2) opposite to the surface where the magnetic
layer (3) is formed.
Comparative Example 4
[0073] A magnetic tape sample was prepared in the same manner as in
Example 1, except for changing the thickness of the metal layer (7)
to 60 nm.
Comparative Example 5
[0074] A magnetic tape sample was prepared in the same manner as in
Example 1, except for changing the thickness of the metal layer (7)
to 100 nm.
[0075] [Running Durability]
[0076] The coefficient of dynamic friction of the back coating
layer surface side of the thus obtained magnetic tape samples was
measured by using a sliding friction coefficient measuring
apparatus as shown schematically in FIG. 3. Referring to FIG. 3,
one end of the magnetic tape sample was attached to a strain gauge
G, and load W was applied in such a manner that the sample may be
brought into contact with the slide pin S. In order to evaluate the
running durability of the magnetic tape, the magnetic tape sample
was repeatedly slid against the slide pin S for 2,000 paths, and
measurements were made on the initial coefficient of friction for
the first path and the final coefficient of friction for the 2000th
path. Further, as an indication of change in the coefficient of
friction, the increase ratio of friction coefficient was calculated
in accordance with equation 1. The generation of flaws on the
sliding surface was observed after the measurement.
Increase ratio of friction coefficient (%)=[(final coefficient of
friction-initial coefficient of friction)/initial coefficient of
friction].times.100 (Equation 1)
[0077] Material of slide pin: SUS303 .phi.2
[0078] Surface property of slide pin: 0.2 S
[0079] Winding angle: 90.degree.
[0080] Sliding speed: 35 mm/s
[0081] Load: 20 gf
[0082] The evaluation of surface flaws was expressed based on the
following standards.
[0083] .largecircle.: No flaws observed.
[0084] .DELTA.: Few flaws are observed, but are of no practical
problem.
[0085] .times.: Considerable amount of flaws are observed.
[0086] The same measurements as above were performed except for
using above SUS303 .phi.2 pin as the slide pin S surface coated
with DLC film.
[0087] (Electromagnetic Conversion Properties]
[0088] By using Mammoth-2 (manufactured by Exabyte Corporation) as
the drive, the following measurements were performed under room
temperature environment (at 20.degree. C., 60%).
[0089] The drive above and the objective tape samples were each set
in the above environment of measuring for 6 hours to be accustomed
to the environment. While recording a sinusoidal wave at 2 T (21
MHz) in the drive by using Write head, reproduction was performed
by using Read head. The reproduction output (RF) from the Read head
was taken out from TP (test point) of the above drive, and the
output for input frequency (21 MHz) was measured using a spectrum
analyzer (Model 4395A manufactured by Agilent Technologies, Inc.).
The measured value was displayed in relative values with respect to
the measured value for the tape sample of Example 1 taken at 0
dB.
[0090] [Short Scale Durability]
[0091] By using Mammoth-2 (manufactured by Exabyte Corporation) as
the drive and Vista (Visual SCSI Test Application) software
provided by Exabyte Corporation, the following operation was
conducted under room temperature environment (at 20.degree. C.,
60%).
[0092] The drive above and the objective tape samples were each set
in the above environment of measuring for 6 hours to be accustomed
to the environment. Random data of 288 Mbyte were undergone
Write/Read process while the tape was run on the drive. The running
pattern was set as such that the (Writing 288 Mbytes of
data.fwdarw.Rewinding.fwdarw.Reading 288 Mbytes of
data.fwdarw.Rewinding) sequence would be repeated. The runs were
counted by incrementing the count per pattern above up to 1000
counts.
[0093] [Measurement of Cupping]
[0094] As shown in FIG. 4, 150 mm long magnetic tape sample was set
with its magnetic layer side surface upward symmetrically on two
supporting points (p) and (p) provided horizontally to right and
left sides at a distance-of 35 mm from each center, and 0.3-g loads
(w) and (w) were each set on the right and left ends of the tape.
This thickness of deformation (mm) of the tape at the midpoint
between the right and left ends was measured by measuring the shade
width of a laser radiation. The thickness of deformation (mm) was
employed as the observed value of cupping. In the case the observed
value is positive, the tape is convex to the magnetic layer side;
in the case the observed value is negative, the tape is convex to
the back coating layer side.
1TABLE 1 Test with metallic pin Flaws Electromagnetic Friction
coefficient by sliding conversion Increase ratio After Short scale
properties Cupping 1 path 2000 paths (%) 2000 paths durability (dB)
(mm) Example 1 0.26 0.35 35 .smallcircle. fine 0 0.1 Example 2 0.23
0.32 39 .smallcircle. fine 0 0.1 Example 3 0.23 0.33 43
.smallcircle. fine 0 0.1 Example 4 0.24 0.35 46 .DELTA. edge damage
-0.2 0.3 Example 5 0.24 0.33 38 .DELTA. edge damage -0.3 0.2
Example 6 0.24 0.32 33 .smallcircle. fine -0.5 -0.3 Comparative
0.26 0.45 73 x running stop 0 0 Example 1 Comparative 0.33 0.46 39
x running stop -0.6 0.5 Example 2 Comparative 0.24 0.39 63 x
running stop 0 -0.1 Example 3 Comparative 0.26 0.39 50 .DELTA.
running stop -0.7 0.6 Example 4 Comparative 0.25 0.40 60 .DELTA.
running stop -1 0.9 Example 5
[0095]
2TABLE 2 Test with DLC-treated metallic pin Electro- Flaws magnetic
Friction coefficient by sliding conversion Increase ratio After
Short scale properties 1 path 2000 paths (%) 2000 paths durability
(dB) Example 1 0.23 0.25 9 .smallcircle. fine 0 Example 2 0.23 0.24
4 .smallcircle. fine 0 Example 3 0.23 0.24 4 .smallcircle. fine 0
Example 4 0.23 0.26 13 .smallcircle. fine -0.2 Example 5 0.23 0.26
13 .smallcircle. fine -0.3 Example 6 0.22 0.23 5 .smallcircle. fine
-0.5 Comparative 0.23 0.30 30 .DELTA. edge damage 0 Example 1
Comparative 0.26 0.32 23 x edge damage -0.6 Example 2 Comparative
0.22 0.36 64 .DELTA. running stop 0 Example 3 Comparative 0.22 0.26
18 .smallcircle. edge damage -0.7 Example 4 Comparative 0.24 0.28
17 .smallcircle. edge damage -1 Example 5
[0096] The results thus obtained are summarized in Table 1 and
Table 2. Table 1 shows the results concerning SUS303 .phi.2 pin.
Table 1 reads that an increase in coefficient of sliding friction
is suppressed for all the tape samples of Examples 1 to 6, and that
no flaws generated on the sliding surface (Examples 1 to 3, and 6)
or that the flaws generated only slightly in a practically
negligible level (Examples 4 and 5). Further, the electromagnetic
conversion properties as well as short scale durability of the
samples were favorable as compared with those of the comparative
examples.
[0097] In comparative examples 1 and 3 having no metal layers, on
the contrary, considerable increase in coefficient of sliding
friction and generation of many flaws on the sliding surface were
observed, and causing running stops. In comparative example 2, in
which back coating layer was missing, many flaws generated on the
sliding surface, and large cupping occurred to cause running stops.
In comparative examples 4 and 5, since the metal layer was too
thick, large cupping occurred to cause running stops, further to
deteriorate electromagnetic conversion properties.
[0098] Table 2 shows the results obtained for the case concerning
DLC-coating treated SUS303 .phi.2 pin. Table 2reads that favorable
results are obtained concerning slide flaws with the sliding pin
DLC-coating treated, except for the sample of comparative example
2. However, by taking the increase ratio in friction coefficient
into consideration, it was found that the samples of the examples
yielded superior results as compared to those of comparative
examples. In the case the slide pins are DLC-coating treated,
considerable differences were also found to occur in the increase
ratio of friction coefficient and running durability depending on
whether metal layer is provided or not.
[0099] On measuring the refractive index of the film formed on an
Si wafer under the same conditions for forming the back coating
layer (DLC film) in each examples and comparative examples by using
an ellipsometer (manufactured by Mizojiri Kogaku Kogyo K. K.),those
values were found to be 2.1. Furthermore, the atomic ratio of
hydrogen to carbon (H/C) measured by means of ERDA (Elastic Recoil
Detection Analysis) was found to be 0.3. Further, it was found that
the back coating layers of each examples and comparative examples
have broad peaks at 1,560 cm.sup.-1 and 1,330 cm.sup.-1 in Raman
spectroscopy.
* * * * *